Add the onion to a large saucepan and cook, stirring frequently, until browned. Add small amounts of water as needed to keep the onion from sticking. Add the garlic, zucchini, squash and mushrooms and saute until the mushrooms begin to exude their juices
Add the oregano, basil, salt and pepper, diced tomatoes, tomato sauce and black olives and cook for 5 minutes over medium heat.
Cook the pasta in boiling water until it is not quite al dente as it will finish cooking in the oven (this is usually a minute or two less than the package cooking instructions would recommend).
Drain the pasta and add it to the tomato mixture. Mix well and pour into a 9x13" baking dish.
Top with the Cheezy Sauce and bake, uncovered, for 25 to 30 minutes, or until bubbly.
Recipe by Plantivores at http://plantivores.com/vegan-baked-ziti/